Several methods and apparatus have been developed for the production of three-dimensional objects by irradiating photopolymer layer upon layer. To provide adequate accuracy of the side surfaces of the objects, the layers must be thin and, hence, in many cases hundreds and thousands of layers of liquid photopolymer must be deposited and irradiated to form an object. In addition, these processes must be fast to assure required productivity. Unfortunately, polymer liquids are quite viscous and their deposition in thin layers by liquid flow can take significant time. Furthermore, distortion during photopolymer solidification has to be minimized.
Forming each layer point by point by irradiation of an open photopolymer surface using a laser as disclosed in U.S. Pat. No. 4,575,330 can be slow and inaccurate due to irradiation by the scanning of a single point at a time, because irradiated polymer is not constrained and warps during irradiation, and since free flow of polymer is used for deposition. The method and apparatus disclosed in my U.S. Pat. No. 4,752,498 for forming whole layers of any size simultaneously while the layer is constrained is free of these drawbacks and provides much higher production rates and accuracy. However, simplification of the apparatus and further improvements in speed and accuracy of fabrication are desirable.
With most known methods, objects are formed in a container filled with a liquid polymer which precludes full cure due to accompanying distortion of underlying preceding layers, and hence necessitates additional cure after the object is formed, as well as the building of supports for overhangs since they are not strong enough to support themselves in the liquid. Postcuring often brings distortion not only through polymer shrinkage but also through warpage which is especially severe in asymmetrical and thin-wall objects.
The formation of objects in containers of liquid makes it difficult to vary polymer material from layer to layer as is required for such objects as aircraft-automobile instrument panels that incorporate several materials with different mechanical, electrical, optical, etc. properties.